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SpaceX Discussion Thread

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4 hours ago, Hannu2 said:

Yes, but those things are significant reasons why current space rovers drive 10 miles per year instead of hour. Average or even top speed of 10 mph is totally unrealistic with current technology.

According to the internet, the top speed of the Lunar Rover is 8 mph and Gene Cernan got it up to 11 (insert "these knobs go to 11" joke). That being said, the 10 mph is with respect to the equator so if you have a cliff in the way, and you have to go perpendicular to the equator, your speed is 0. So yeah, 10 mph average speed is pretty high depending on how much backtracking you have to do. Although, this is only on the equator, the distance to travel is much less at higher latitudes. 

The part of me that has done off road racing is going "Baja average speed is like 50 mph for top teams..." but that's in a trophy truck that can do 100+ off road over a route that the obstacles are already known.

Back on topic a little bit: FH to Pluto. Flyby: sure, KSP has taught me well that flybys are easy. Orbiter: if you don't mind waiting: maybe. If you do mind waiting: not with current technology.

Based on the Ice Giant mission proposal by JPL, there are several limitations to current technology.

  • First, FH simply doesn't have the payload capacity to launch an orbiter probe that follows a New Horizons trajectory in a single launch. New Horizons would have had to scrub in the neighborhood of 14 km/s to get into orbit.
  • What about using electric propulsion? Well, the Ice Giant's mission discusses that. For the Uranus orbiter with no atmospheric probe, they proposed using a Solar Electric Propulsion module to gain some energy in the inner solar system before moving out to the gas planets. Unfortunately, this required a 30 kW power system, only gets 5.6 km/s of dV and only works in the inner solar system. Currently, even Kilopower isn't enough (plus it weighs too much) to power something like this.
  • Nuclear propulsion? There is a minimum size to a functioning NTR: 1770 kg plus the added challenge of trying to store hydrogen for 9ish years. What about with other propellants? I've looked into it and it's simply not feasible on a small scale. With a bigger launch mass, maybe. 
  • In-space refueling? Now we're talking... although this is something that would fall under new technology. 

I think it's possible to get an orbiter to Pluto in a reasonable amount of time. In fact, using FH is a reasonable choice to do so. However, new technology needs to be proven out before it can become a reality. I would like to see cryogenic prop transfer, long term cryogenic fuel storage, and NTRs get proven out to make this a reality. Otherwise, it just takes a huge rocket to do it all at once with something that's easy to store. Enter: BFR.

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2 hours ago, Wjolcz said:

How do you guys think people will move around BFS? It looks spacious so I would guess some sort of temprorary nets would have to be there just so people don't get stuck in the middle of the big room (I guess you could call it a room, right?). Either that or some sort of personal device to move around, like a hand-held fan or a CO2 thruster. I'm guessing since there will be CO2 scrubbers/filters then it won't be dangerous to use something like that. But then collecting CO2 for refilling would probably be more complicated than just charging batteries of a "fan gun".

How about a 15 minute training video on using breath thrust.

The average person breathes 7-8 liters/min or ~0.25 kg at seal-level

Which can apparently be accelerated to > 40m/s : https://www.quora.com/What-is-the-maximum-air-velocity-which-can-reached-by-blowing-by-mouth

Allowing an acceleration of about 0.1m/s/min for a 100kg human by just exhaling through their mouth with pursed lips.

Pretty lousy for a space-craft, but pretty tolerable for the rare occasion of getting stuck a meter or two away form the nearest hand-hold should no one be around to help.

 

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42 minutes ago, Racescort666 said:

According to the internet, the top speed of the Lunar Rover is 8 mph and Gene Cernan got it up to 11 (insert "these knobs go to 11" joke). That being said, the 10 mph is with respect to the equator so if you have a cliff in the way, and you have to go perpendicular to the equator, your speed is 0. So yeah, 10 mph average speed is pretty high depending on how much backtracking you have to do. Although, this is only on the equator, the distance to travel is much less at higher latitudes. 

The part of me that has done off road racing is going "Baja average speed is like 50 mph for top teams..." but that's in a trophy truck that can do 100+ off road over a route that the obstacles are already known.

 

Hom much would the orbital surveys we've done help? Are they a good enough resolution to avoid the worst obsticals?

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Spoiler

Btw a must have thing for zero/low-G conditions.

Also to move around BFS

Spoiler

s-l640.jpgfaij19.jpg

 

 

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52 minutes ago, Steel said:

LRO images have a resolution of about 100 m [1]. So the short answer to how much it would help is "not much".

 

[1] https://en.wikipedia.org/wiki/Lunar_Reconnaissance_Orbiter

That's the 3d map of the entire surface (except for the polar areas in shadow). It's capable of higher resolution. The Apollo sites have 0.5 meters per pixel.

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37 minutes ago, Rakaydos said:

Hom much would the orbital surveys we've done help? Are they a good enough resolution to avoid the worst obsticals?

At a high level (figuratively and literally) you could use the orbital surveys to plot a basic route. This is kind of how they plan roads with a topographic map. Simply having a road wouldn't be enough to say that you could drive flat-out though. 

Stuff like this: you can drive over but not fast and certainly not at 10 mph and you won't be able to see it easily from an aerial photo:

21652582662_7fbb1ba403_o.jpg

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5 hours ago, Racescort666 said:

Back on topic a little bit: FH to Pluto. Flyby: sure, KSP has taught me well that flybys are easy. Orbiter: if you don't mind waiting: maybe. If you do mind waiting: not with current technology.

Based on the Ice Giant mission proposal by JPL, there are several limitations to current technology.

  • First, FH simply doesn't have the payload capacity to launch an orbiter probe that follows a New Horizons trajectory in a single launch. New Horizons would have had to scrub in the neighborhood of 14 km/s to get into orbit.
  • What about using electric propulsion? Well, the Ice Giant's mission discusses that. For the Uranus orbiter with no atmospheric probe, they proposed using a Solar Electric Propulsion module to gain some energy in the inner solar system before moving out to the gas planets. Unfortunately, this required a 30 kW power system, only gets 5.6 km/s of dV and only works in the inner solar system. Currently, even Kilopower isn't enough (plus it weighs too much) to power something like this.
  • Nuclear propulsion? There is a minimum size to a functioning NTR: 1770 kg plus the added challenge of trying to store hydrogen for 9ish years. What about with other propellants? I've looked into it and it's simply not feasible on a small scale. With a bigger launch mass, maybe. 
  • In-space refueling? Now we're talking... although this is something that would fall under new technology. 

I think it's possible to get an orbiter to Pluto in a reasonable amount of time. In fact, using FH is a reasonable choice to do so. However, new technology needs to be proven out before it can become a reality. I would like to see cryogenic prop transfer, long term cryogenic fuel storage, and NTRs get proven out to make this a reality. Otherwise, it just takes a huge rocket to do it all at once with something that's easy to store. Enter: BFR.

I wonder if Uranus or Neptune are lined up for a relative-velocity-cancelling slingshot.

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5 hours ago, sevenperforce said:

I wonder if Uranus or Neptune are lined up for a relative-velocity-cancelling slingshot.

Lets test that in ksp.

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5 hours ago, Xd the great said:

Lets test that in ksp.

Doing that in a reasonable dV efficient way would mean 100+ years travel time from Uranus to Pluto.

We are talking about planets with orbital periods of 84 and 250 years here...

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9 hours ago, Nefrums said:

Doing that in a reasonable dV efficient way would mean 100+ years travel time from Uranus to Pluto.

We are talking about planets with orbital periods of 84 and 250 years here...

It doesnt have to be a low energy transfer, it just has to take the worst edge off orbital capture.

Starting from a 1 AU hyperbola, a Uranus  flyby that turns it into an elyptical orbit with a low point around Saturn and a high point around Sedna or so is still decently fast, but easier to reach pluto orbit from a flyby.

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On 8/22/2018 at 6:24 PM, kerbiloid said:

faij19.jpg

Indiana Jones was originally a Marvel Comic!?!?

On 8/22/2018 at 10:37 PM, sevenperforce said:

I wonder if Uranus or Neptune are lined up for a relative-velocity-cancelling slingshot.

https://trajbrowser.arc.nasa.gov/traj_browser.php

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21 minutes ago, DAL59 said:

Indiana Jones was originally a Marvel Comic!?!?

Spoiler

And now he’s dust in the wind... <_<

 

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I was worried for a second there that they are planning to catch rocket parts with a helicopter because fairing recoveries aren't successful enough, or something. Not like it would be a bad thing but catching it in a net seems way more cost effective.

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46 minutes ago, Wjolcz said:

I was worried for a second there that they are planning to catch rocket parts with a helicopter because fairing recoveries aren't successful enough, or something. Not like it would be a bad thing but catching it in a net seems way more cost effective.

I mean... that's ULA's plan...

20150413_ula-smart-system.jpg

Also, this was the original graphic (and the most amazing graphic I've seen in a formal presentation):

recovery.jpg

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It's to move astronauts ashore faster than the days it might take aboard ship.

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"Helicopter Acquisition Trailing Line Engagement"

Pure hate.

 

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"Sustainably collapsing..." Really ULA? Really? Into a singularity, eventually? That's the worst piece of presentation lingo i've seen in a long time.

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I imagine recertify/reattach are non-trivial costs.

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4 hours ago, tater said:

I imagine recertify/reattach are non-trivial costs.

Also, the cost of that high-tech inflatable heat shield of theirs...

Anyone in here know of a suitably durable and flexible material to use for something like that? It looks like they're planning to completely chuck it after every flight, which can't be cheap. Honestly, I'm starting to think that the main motivation behind SMART reuse is to avoid bottlenecks on engine production, considering the turtle's snail's pace Blue Origin moves at.

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Notice the term "Smart reuse".  I fail to see how recovering only 2/3rds of the booster's cost (the added complexity of dropping the engine probably also adds significant extra costs to each booster, and possibly even new launch failure modes) qualifies as "smart reuse".  This ULA scheme looks like a poor second cousin to SpaceX current program of Falcon 9 booster landing and re-use.  And there a fair chance that it won't be operational before SpaceX is launching BFR, (which should be full reuse of both first and second stages).  At that point SpaceX is probably about to retire the Falcon 9, (which is already flying as a superior example of reuse), leaving ULA still trailing by one and a half generations.  If you are going to do a reusable booster, then landing the booster seems superior and smarter in every way.

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It’s not always possible to land a booster like SpaceX does. If you have a single powerful engine like RD-180 that can’t throttle down that deeply, or even be restarted, then recovering just the engine is your best option, still better than no reuse.

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